Musnad Ahmad 30:1471

Hassan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, Abu al-Aswad narrated to us, from Yahya ibn al-Nadr, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The rural lands will be opened, and people will come to their acquaintances and go with them, while Medina is better for them if they only knew." He said it twice.